Re: [PATCH v6 2/6] drm/panfrost: Add fdinfo support GPU load metrics

From: Adrián Larumbe
Date: Fri Sep 22 2023 - 06:57:19 EST

On 20.09.2023 16:40, Tvrtko Ursulin wrote:
>On 20/09/2023 00:34, Adrián Larumbe wrote:
>> The drm-stats fdinfo tags made available to user space are drm-engine,
>> drm-cycles, drm-max-freq and drm-curfreq, one per job slot.
>>
>> This deviates from standard practice in other DRM drivers, where a single
>> set of key:value pairs is provided for the whole render engine. However,
>> Panfrost has separate queues for fragment and vertex/tiler jobs, so a
>> decision was made to calculate bus cycles and workload times separately.
>>
>> Maximum operating frequency is calculated at devfreq initialisation time.
>> Current frequency is made available to user space because nvtop uses it
>> when performing engine usage calculations.
>>
>> It is important to bear in mind that both GPU cycle and kernel time numbers
>> provided are at best rough estimations, and always reported in excess from
>> the actual figure because of two reasons:
>> - Excess time because of the delay between the end of a job processing,
>> the subsequent job IRQ and the actual time of the sample.
>> - Time spent in the engine queue waiting for the GPU to pick up the next
>> job.
>>
>> To avoid race conditions during enablement/disabling, a reference counting
>> mechanism was introduced, and a job flag that tells us whether a given job
>> increased the refcount. This is necessary, because user space can toggle
>> cycle counting through a debugfs file, and a given job might have been in
>> flight by the time cycle counting was disabled.
>>
>> The main goal of the debugfs cycle counter knob is letting tools like nvtop
>> or IGT's gputop switch it at any time, to avoid power waste in case no
>> engine usage measuring is necessary.
>>
>> Signed-off-by: Adrián Larumbe <adrian.larumbe@xxxxxxxxxxxxx>
>> Reviewed-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
>> Reviewed-by: Steven Price <steven.price@xxxxxxx>
>> ---
>> drivers/gpu/drm/panfrost/Makefile | 2 +
>> drivers/gpu/drm/panfrost/panfrost_debugfs.c | 20 ++++++++
>> drivers/gpu/drm/panfrost/panfrost_debugfs.h | 13 +++++
>> drivers/gpu/drm/panfrost/panfrost_devfreq.c | 8 +++
>> drivers/gpu/drm/panfrost/panfrost_devfreq.h | 3 ++
>> drivers/gpu/drm/panfrost/panfrost_device.c | 2 +
>> drivers/gpu/drm/panfrost/panfrost_device.h | 13 +++++
>> drivers/gpu/drm/panfrost/panfrost_drv.c | 57 ++++++++++++++++++++-
>> drivers/gpu/drm/panfrost/panfrost_gpu.c | 41 +++++++++++++++
>> drivers/gpu/drm/panfrost/panfrost_gpu.h | 4 ++
>> drivers/gpu/drm/panfrost/panfrost_job.c | 24 +++++++++
>> drivers/gpu/drm/panfrost/panfrost_job.h | 5 ++
>> 12 files changed, 191 insertions(+), 1 deletion(-)
>> create mode 100644 drivers/gpu/drm/panfrost/panfrost_debugfs.c
>> create mode 100644 drivers/gpu/drm/panfrost/panfrost_debugfs.h
>>
>> diff --git a/drivers/gpu/drm/panfrost/Makefile b/drivers/gpu/drm/panfrost/Makefile
>> index 7da2b3f02ed9..2c01c1e7523e 100644
>> --- a/drivers/gpu/drm/panfrost/Makefile
>> +++ b/drivers/gpu/drm/panfrost/Makefile
>> @@ -12,4 +12,6 @@ panfrost-y := \
>> panfrost_perfcnt.o \
>> panfrost_dump.o
>> +panfrost-$(CONFIG_DEBUG_FS) += panfrost_debugfs.o
>> +
>> obj-$(CONFIG_DRM_PANFROST) += panfrost.o
>> diff --git a/drivers/gpu/drm/panfrost/panfrost_debugfs.c b/drivers/gpu/drm/panfrost/panfrost_debugfs.c
>> new file mode 100644
>> index 000000000000..cc14eccba206
>> --- /dev/null
>> +++ b/drivers/gpu/drm/panfrost/panfrost_debugfs.c
>> @@ -0,0 +1,20 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/* Copyright 2023 Collabora ltd. */
>> +
>> +#include <linux/debugfs.h>
>> +#include <linux/platform_device.h>
>> +#include <drm/drm_debugfs.h>
>> +#include <drm/drm_file.h>
>> +#include <drm/panfrost_drm.h>
>> +
>> +#include "panfrost_device.h"
>> +#include "panfrost_gpu.h"
>> +#include "panfrost_debugfs.h"
>> +
>> +void panfrost_debugfs_init(struct drm_minor *minor)
>> +{
>> + struct drm_device *dev = minor->dev;
>> + struct panfrost_device *pfdev = platform_get_drvdata(to_platform_device(dev->dev));
>> +
>> + debugfs_create_atomic_t("profile", 0600, minor->debugfs_root, &pfdev->profile_mode);
>> +}
>> diff --git a/drivers/gpu/drm/panfrost/panfrost_debugfs.h b/drivers/gpu/drm/panfrost/panfrost_debugfs.h
>> new file mode 100644
>> index 000000000000..db1c158bcf2f
>> --- /dev/null
>> +++ b/drivers/gpu/drm/panfrost/panfrost_debugfs.h
>> @@ -0,0 +1,13 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +/*
>> + * Copyright 2023 Collabora ltd.
>> + */
>> +
>> +#ifndef PANFROST_DEBUGFS_H
>> +#define PANFROST_DEBUGFS_H
>> +
>> +#ifdef CONFIG_DEBUG_FS
>> +void panfrost_debugfs_init(struct drm_minor *minor);
>> +#endif
>> +
>> +#endif /* PANFROST_DEBUGFS_H */
>> diff --git a/drivers/gpu/drm/panfrost/panfrost_devfreq.c b/drivers/gpu/drm/panfrost/panfrost_devfreq.c
>> index 58dfb15a8757..28caffc689e2 100644
>> --- a/drivers/gpu/drm/panfrost/panfrost_devfreq.c
>> +++ b/drivers/gpu/drm/panfrost/panfrost_devfreq.c
>> @@ -58,6 +58,7 @@ static int panfrost_devfreq_get_dev_status(struct device *dev,
>> spin_lock_irqsave(&pfdevfreq->lock, irqflags);
>> panfrost_devfreq_update_utilization(pfdevfreq);
>> + pfdevfreq->current_frequency = status->current_frequency;
>> status->total_time = ktime_to_ns(ktime_add(pfdevfreq->busy_time,
>> pfdevfreq->idle_time));
>> @@ -117,6 +118,7 @@ int panfrost_devfreq_init(struct panfrost_device *pfdev)
>> struct devfreq *devfreq;
>> struct thermal_cooling_device *cooling;
>> struct panfrost_devfreq *pfdevfreq = &pfdev->pfdevfreq;
>> + unsigned long freq = ULONG_MAX;
>> if (pfdev->comp->num_supplies > 1) {
>> /*
>> @@ -172,6 +174,12 @@ int panfrost_devfreq_init(struct panfrost_device *pfdev)
>> return ret;
>> }
>> + /* Find the fastest defined rate */
>> + opp = dev_pm_opp_find_freq_floor(dev, &freq);
>> + if (IS_ERR(opp))
>> + return PTR_ERR(opp);
>> + pfdevfreq->fast_rate = freq;
>> +
>> dev_pm_opp_put(opp);
>> /*
>> diff --git a/drivers/gpu/drm/panfrost/panfrost_devfreq.h b/drivers/gpu/drm/panfrost/panfrost_devfreq.h
>> index 1514c1f9d91c..48dbe185f206 100644
>> --- a/drivers/gpu/drm/panfrost/panfrost_devfreq.h
>> +++ b/drivers/gpu/drm/panfrost/panfrost_devfreq.h
>> @@ -19,6 +19,9 @@ struct panfrost_devfreq {
>> struct devfreq_simple_ondemand_data gov_data;
>> bool opp_of_table_added;
>> + unsigned long current_frequency;
>> + unsigned long fast_rate;
>> +
>> ktime_t busy_time;
>> ktime_t idle_time;
>> ktime_t time_last_update;
>> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.c b/drivers/gpu/drm/panfrost/panfrost_device.c
>> index fa1a086a862b..28f7046e1b1a 100644
>> --- a/drivers/gpu/drm/panfrost/panfrost_device.c
>> +++ b/drivers/gpu/drm/panfrost/panfrost_device.c
>> @@ -207,6 +207,8 @@ int panfrost_device_init(struct panfrost_device *pfdev)
>> spin_lock_init(&pfdev->as_lock);
>> + spin_lock_init(&pfdev->cycle_counter.lock);
>> +
>> err = panfrost_clk_init(pfdev);
>> if (err) {
>> dev_err(pfdev->dev, "clk init failed %d\n", err);
>> diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h b/drivers/gpu/drm/panfrost/panfrost_device.h
>> index b0126b9fbadc..1e85656dc2f7 100644
>> --- a/drivers/gpu/drm/panfrost/panfrost_device.h
>> +++ b/drivers/gpu/drm/panfrost/panfrost_device.h
>> @@ -107,6 +107,7 @@ struct panfrost_device {
>> struct list_head scheduled_jobs;
>> struct panfrost_perfcnt *perfcnt;
>> + atomic_t profile_mode;
>> struct mutex sched_lock;
>> @@ -121,6 +122,11 @@ struct panfrost_device {
>> struct shrinker shrinker;
>> struct panfrost_devfreq pfdevfreq;
>> +
>> + struct {
>> + atomic_t use_count;
>> + spinlock_t lock;
>> + } cycle_counter;
>> };
>> struct panfrost_mmu {
>> @@ -135,12 +141,19 @@ struct panfrost_mmu {
>> struct list_head list;
>> };
>> +struct panfrost_engine_usage {
>> + unsigned long long elapsed_ns[NUM_JOB_SLOTS];
>> + unsigned long long cycles[NUM_JOB_SLOTS];
>> +};
>> +
>> struct panfrost_file_priv {
>> struct panfrost_device *pfdev;
>> struct drm_sched_entity sched_entity[NUM_JOB_SLOTS];
>> struct panfrost_mmu *mmu;
>> +
>> + struct panfrost_engine_usage engine_usage;
>> };
>> static inline struct panfrost_device *to_panfrost_device(struct drm_device *ddev)
>> diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
>> index a2ab99698ca8..3c93a11deab1 100644
>> --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
>> +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
>> @@ -20,6 +20,7 @@
>> #include "panfrost_job.h"
>> #include "panfrost_gpu.h"
>> #include "panfrost_perfcnt.h"
>> +#include "panfrost_debugfs.h"
>> static bool unstable_ioctls;
>> module_param_unsafe(unstable_ioctls, bool, 0600);
>> @@ -267,6 +268,7 @@ static int panfrost_ioctl_submit(struct drm_device *dev, void *data,
>> job->requirements = args->requirements;
>> job->flush_id = panfrost_gpu_get_latest_flush_id(pfdev);
>> job->mmu = file_priv->mmu;
>> + job->engine_usage = &file_priv->engine_usage;
>> slot = panfrost_job_get_slot(job);
>> @@ -523,7 +525,55 @@ static const struct drm_ioctl_desc panfrost_drm_driver_ioctls[] = {
>> PANFROST_IOCTL(MADVISE, madvise, DRM_RENDER_ALLOW),
>> };
>> -DEFINE_DRM_GEM_FOPS(panfrost_drm_driver_fops);
>> +
>> +static void panfrost_gpu_show_fdinfo(struct panfrost_device *pfdev,
>> + struct panfrost_file_priv *panfrost_priv,
>> + struct drm_printer *p)
>> +{
>> + int i;
>> +
>> + /*
>> + * IMPORTANT NOTE: drm-cycles and drm-engine measurements are not
>> + * accurate, as they only provide a rough estimation of the number of
>> + * GPU cycles and CPU time spent in a given context. This is due to two
>> + * different factors:
>> + * - Firstly, we must consider the time the CPU and then the kernel
>> + * takes to process the GPU interrupt, which means additional time and
>> + * GPU cycles will be added in excess to the real figure.
>> + * - Secondly, the pipelining done by the Job Manager (2 job slots per
>> + * engine) implies there is no way to know exactly how much time each
>> + * job spent on the GPU.
>> + */
>> +
>> + static const char * const engine_names[] = {
>> + "fragment", "vertex-tiler", "compute-only"
>> + };
>> +
>> + for (i = 0; i < NUM_JOB_SLOTS - 1; i++) {
>
>FWIW you could future proof this a bit by using "i < ARRAY_SIZE(engine_names)"
>and avoid maybe silent out of bounds reads if someone updates NUM_JOB_SLOTS
>and forgets about this loop. Or stick a warning of some sort.
>
NUM_JOB_SLOTS is actually the same as the number of engines in the device. I decided to follow
this loop convention because that's what's being done across the driver when manipulating
the engine queues, so I thought I'd stick to it for the sake of consistency. Bear in mind
the loop doesn't pick up the compute-only engine because it's still not exposed to user space.

So NUM_JOB_SLOTS cannot change, unless a new engine were introduced, and then someone would
have to update this array accordingly.

>> + drm_printf(p, "drm-engine-%s:\t%llu ns\n",
>> + engine_names[i], panfrost_priv->engine_usage.elapsed_ns[i]);
>> + drm_printf(p, "drm-cycles-%s:\t%llu\n",
>> + engine_names[i], panfrost_priv->engine_usage.cycles[i]);
>> + drm_printf(p, "drm-maxfreq-%s:\t%lu Hz\n",
>> + engine_names[i], pfdev->pfdevfreq.fast_rate);
>> + drm_printf(p, "drm-curfreq-%s:\t%lu Hz\n",
>> + engine_names[i], pfdev->pfdevfreq.current_frequency);
>
>I envisaged a link to driver specific docs at the bottom of
>drm-usage-stats.rst so it would be nice if drivers would be adding those
>sections and describing their private keys, engine names etc. ;)
>
Currently there's no panfrost.rst file under Documentation/gpu. I guess I'll create a new
one and add the engine descriptions and meaning of drm-curfreq key.

>Regards,
>
>Tvrtko
>
>> + }
>> +}
>> +
>> +static void panfrost_show_fdinfo(struct drm_printer *p, struct drm_file *file)
>> +{
>> + struct drm_device *dev = file->minor->dev;
>> + struct panfrost_device *pfdev = dev->dev_private;
>> +
>> + panfrost_gpu_show_fdinfo(pfdev, file->driver_priv, p);
>> +}
>> +
>> +static const struct file_operations panfrost_drm_driver_fops = {
>> + .owner = THIS_MODULE,
>> + DRM_GEM_FOPS,
>> + .show_fdinfo = drm_show_fdinfo,
>> +};
>> /*
>> * Panfrost driver version:
>> @@ -535,6 +585,7 @@ static const struct drm_driver panfrost_drm_driver = {
>> .driver_features = DRIVER_RENDER | DRIVER_GEM | DRIVER_SYNCOBJ,
>> .open = panfrost_open,
>> .postclose = panfrost_postclose,
>> + .show_fdinfo = panfrost_show_fdinfo,
>> .ioctls = panfrost_drm_driver_ioctls,
>> .num_ioctls = ARRAY_SIZE(panfrost_drm_driver_ioctls),
>> .fops = &panfrost_drm_driver_fops,
>> @@ -546,6 +597,10 @@ static const struct drm_driver panfrost_drm_driver = {
>> .gem_create_object = panfrost_gem_create_object,
>> .gem_prime_import_sg_table = panfrost_gem_prime_import_sg_table,
>> +
>> +#ifdef CONFIG_DEBUG_FS
>> + .debugfs_init = panfrost_debugfs_init,
>> +#endif
>> };
>> static int panfrost_probe(struct platform_device *pdev)
>> diff --git a/drivers/gpu/drm/panfrost/panfrost_gpu.c b/drivers/gpu/drm/panfrost/panfrost_gpu.c
>> index 2faa344d89ee..f0be7e19b13e 100644
>> --- a/drivers/gpu/drm/panfrost/panfrost_gpu.c
>> +++ b/drivers/gpu/drm/panfrost/panfrost_gpu.c
>> @@ -73,6 +73,13 @@ int panfrost_gpu_soft_reset(struct panfrost_device *pfdev)
>> gpu_write(pfdev, GPU_INT_CLEAR, GPU_IRQ_MASK_ALL);
>> gpu_write(pfdev, GPU_INT_MASK, GPU_IRQ_MASK_ALL);
>> + /*
>> + * All in-flight jobs should have released their cycle
>> + * counter references upon reset, but let us make sure
>> + */
>> + if (drm_WARN_ON(pfdev->ddev, atomic_read(&pfdev->cycle_counter.use_count) != 0))
>> + atomic_set(&pfdev->cycle_counter.use_count, 0);
>> +
>> return 0;
>> }
>> @@ -321,6 +328,40 @@ static void panfrost_gpu_init_features(struct panfrost_device *pfdev)
>> pfdev->features.shader_present, pfdev->features.l2_present);
>> }
>> +void panfrost_cycle_counter_get(struct panfrost_device *pfdev)
>> +{
>> + if (atomic_inc_not_zero(&pfdev->cycle_counter.use_count))
>> + return;
>> +
>> + spin_lock(&pfdev->cycle_counter.lock);
>> + if (atomic_inc_return(&pfdev->cycle_counter.use_count) == 1)
>> + gpu_write(pfdev, GPU_CMD, GPU_CMD_CYCLE_COUNT_START);
>> + spin_unlock(&pfdev->cycle_counter.lock);
>> +}
>> +
>> +void panfrost_cycle_counter_put(struct panfrost_device *pfdev)
>> +{
>> + if (atomic_add_unless(&pfdev->cycle_counter.use_count, -1, 1))
>> + return;
>> +
>> + spin_lock(&pfdev->cycle_counter.lock);
>> + if (atomic_dec_return(&pfdev->cycle_counter.use_count) == 0)
>> + gpu_write(pfdev, GPU_CMD, GPU_CMD_CYCLE_COUNT_STOP);
>> + spin_unlock(&pfdev->cycle_counter.lock);
>> +}
>> +
>> +unsigned long long panfrost_cycle_counter_read(struct panfrost_device *pfdev)
>> +{
>> + u32 hi, lo;
>> +
>> + do {
>> + hi = gpu_read(pfdev, GPU_CYCLE_COUNT_HI);
>> + lo = gpu_read(pfdev, GPU_CYCLE_COUNT_LO);
>> + } while (hi != gpu_read(pfdev, GPU_CYCLE_COUNT_HI));
>> +
>> + return ((u64)hi << 32) | lo;
>> +}
>> +
>> void panfrost_gpu_power_on(struct panfrost_device *pfdev)
>> {
>> int ret;
>> diff --git a/drivers/gpu/drm/panfrost/panfrost_gpu.h b/drivers/gpu/drm/panfrost/panfrost_gpu.h
>> index 468c51e7e46d..876fdad9f721 100644
>> --- a/drivers/gpu/drm/panfrost/panfrost_gpu.h
>> +++ b/drivers/gpu/drm/panfrost/panfrost_gpu.h
>> @@ -16,6 +16,10 @@ int panfrost_gpu_soft_reset(struct panfrost_device *pfdev);
>> void panfrost_gpu_power_on(struct panfrost_device *pfdev);
>> void panfrost_gpu_power_off(struct panfrost_device *pfdev);
>> +void panfrost_cycle_counter_get(struct panfrost_device *pfdev);
>> +void panfrost_cycle_counter_put(struct panfrost_device *pfdev);
>> +unsigned long long panfrost_cycle_counter_read(struct panfrost_device *pfdev);
>> +
>> void panfrost_gpu_amlogic_quirk(struct panfrost_device *pfdev);
>> #endif
>> diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
>> index 033f5e684707..fb16de2d0420 100644
>> --- a/drivers/gpu/drm/panfrost/panfrost_job.c
>> +++ b/drivers/gpu/drm/panfrost/panfrost_job.c
>> @@ -159,6 +159,16 @@ panfrost_dequeue_job(struct panfrost_device *pfdev, int slot)
>> struct panfrost_job *job = pfdev->jobs[slot][0];
>> WARN_ON(!job);
>> + if (job->is_profiled) {
>> + if (job->engine_usage) {
>> + job->engine_usage->elapsed_ns[slot] +=
>> + ktime_to_ns(ktime_sub(ktime_get(), job->start_time));
>> + job->engine_usage->cycles[slot] +=
>> + panfrost_cycle_counter_read(pfdev) - job->start_cycles;
>> + }
>> + panfrost_cycle_counter_put(job->pfdev);
>> + }
>> +
>> pfdev->jobs[slot][0] = pfdev->jobs[slot][1];
>> pfdev->jobs[slot][1] = NULL;
>> @@ -233,6 +243,13 @@ static void panfrost_job_hw_submit(struct panfrost_job *job, int js)
>> subslot = panfrost_enqueue_job(pfdev, js, job);
>> /* Don't queue the job if a reset is in progress */
>> if (!atomic_read(&pfdev->reset.pending)) {
>> + if (atomic_read(&pfdev->profile_mode)) {
>> + panfrost_cycle_counter_get(pfdev);
>> + job->is_profiled = true;
>> + job->start_time = ktime_get();
>> + job->start_cycles = panfrost_cycle_counter_read(pfdev);
>> + }
>> +
>> job_write(pfdev, JS_COMMAND_NEXT(js), JS_COMMAND_START);
>> dev_dbg(pfdev->dev,
>> "JS: Submitting atom %p to js[%d][%d] with head=0x%llx AS %d",
>> @@ -660,10 +677,14 @@ panfrost_reset(struct panfrost_device *pfdev,
>> * stuck jobs. Let's make sure the PM counters stay balanced by
>> * manually calling pm_runtime_put_noidle() and
>> * panfrost_devfreq_record_idle() for each stuck job.
>> + * Let's also make sure the cycle counting register's refcnt is
>> + * kept balanced to prevent it from running forever
>> */
>> spin_lock(&pfdev->js->job_lock);
>> for (i = 0; i < NUM_JOB_SLOTS; i++) {
>> for (j = 0; j < ARRAY_SIZE(pfdev->jobs[0]) && pfdev->jobs[i][j]; j++) {
>> + if (pfdev->jobs[i][j]->is_profiled)
>> + panfrost_cycle_counter_put(pfdev->jobs[i][j]->pfdev);
>> pm_runtime_put_noidle(pfdev->dev);
>> panfrost_devfreq_record_idle(&pfdev->pfdevfreq);
>> }
>> @@ -926,6 +947,9 @@ void panfrost_job_close(struct panfrost_file_priv *panfrost_priv)
>> }
>> job_write(pfdev, JS_COMMAND(i), cmd);
>> +
>> + /* Jobs can outlive their file context */
>> + job->engine_usage = NULL;
>> }
>> }
>> spin_unlock(&pfdev->js->job_lock);
>> diff --git a/drivers/gpu/drm/panfrost/panfrost_job.h b/drivers/gpu/drm/panfrost/panfrost_job.h
>> index 8becc1ba0eb9..17ff808dba07 100644
>> --- a/drivers/gpu/drm/panfrost/panfrost_job.h
>> +++ b/drivers/gpu/drm/panfrost/panfrost_job.h
>> @@ -32,6 +32,11 @@ struct panfrost_job {
>> /* Fence to be signaled by drm-sched once its done with the job */
>> struct dma_fence *render_done_fence;
>> +
>> + struct panfrost_engine_usage *engine_usage;
>> + bool is_profiled;
>> + ktime_t start_time;
>> + u64 start_cycles;
>> };
>> int panfrost_job_init(struct panfrost_device *pfdev);